Tube amp build (s)

[Marcel]

That's really good to know, thanks Marcel (where would I be without you!)

I actually didn't know those switches existed - I assume you mean one like this? - https://au.rs-online.com/web/p/toggle-switches/8610298

Yes, The switch in the link complies due the barrier between the two sets of spade terminals.

[JohnH]

(you're going to need a purple tolex extension cabinet now)

I've been seriously thinking about it!

Yes, The switch in the link complies due the barrier between the two sets of spade terminals.

Excellent, thanks Marcel. I'll make sure I get one

[JohnH]

What's the saying - perfect is the enemy of done? Well that is totally what I've been doing with this build. I literally have everything on hand to wire it up but kept getting held up fiddling around with faceplate designs because I don't like the ones that came with the chassis.

I decided that was crazy, and am back at it.

[JohnH]

A colleague picked up a fantastic 1961 Vibralux and it led me down a bit of a rabbit hole, but it's got me planning a vibrochamp build. I already have the sockets, switches, and caps/resistors on hand, as well as most of the pots and a tag board I think will work.

I figure an upcoming birthday might be a solution to sourcing some or all of the more expensive tubes/transformers/chassis

[Simon Barden]

I have an 82 Vibro Champ and TBH, it’s a bit ‘meh’. A lot is down to the 8” speaker. It has got an upgraded WGS alnico speaker in it as the original was terrible and broke up and made farting noises at any reasonable volume. However, it’s designed for a 4 ohm load, so finding a single 10” or 12” could be hard. 2x10” maybe if using an original style output transformer?

Really could do with some built-in reverb IMO, which I’d much prefer to having tremolo.

[Simon Barden]

I can’t see an output transformer in that layout diagram, and all the originals certainly have one.

[JohnH]

That's good to know Simon. It seems from what I've been reading that the speakers make a huge difference (unsurprisingly)

I'm not sure what you mean about the layout missing the OT? The wires are either side of the 6V6, unless I'm misunderstanding you?

It definitely isn't the clearest layout though. From what I was reading the circuit never changed, so sometimes layouts fail to mention things like filter cap values or OT values because they are always the same as the original.

I haven't actually gone through the schematic and layout to check yet, but will work from the schematic in any case

[JohnH]

I should also mention that I'm not particularly interested in getting an amazing playing amp from the vibrochamp build, but really want to have a small relatively simple amp circuit to play around with.

I'm treating the amp builds the same way I have been treating the pedal builds - each one should be more complex than the last, or teach me something new. So, the vibrochamp is pretty simple in terms of components but it has the vibrato and if I build it into a larger box I have room to play around - make a list of amp mods and just work my way through.

For example, I'd like to add reverb. Not because I think it'll sound amazing, but because I'd like to understand reverb circuits better - what are the options, how do they work, how are they each different, what will or won't work with this circuit and why, etc

If I end up with an ok amp at the end, then great! But I have heaps of amps now and really just want to understand the circuits better. I figure worst case I make an awful amp but learn some things, then can strip it down for parts for future builds

[Simon Barden]

If you can’t see that what should be an output transformer on the Triode schematic is a capacitor symbol (one of the big filter caps) and that there are only output wires to it, no input ones (so it’s not just a misused symbol), then can I suggest that for safety’s sake you probably need to read up more on valve circuits, so you get to the point where you can. They are not things to take lightly.

Not being fully up on circuit design is OK if you are assembling a good kit with clear instructions, but if that Triode diagram was supplied with a kit, then it’s bad and dangerous. So you first need to know the difference between good and bad.

Referring back to the original schematics is definitely good, so try going through the Triode schematic following the Fender schematic and see how close they are and where the Triode goes wrong.

Don’t take this the wrong way. I just don’t want you blowing yourself up or electrocuting yourself!

For a small amp, I’d personally either go Tweed champ (a bit more character to the sound IMO) or a Princeton circuit of some sort. I’ve always liked Princetons whenever I’ve played one.

[JohnH]

Sorry, but I still don't understand why you think there isn't an OT on that triode layout - there is a 20/20/20 cap can (unlabelled, as I mentioned in a previous post, and which you seem to be suggesting is being used as the symbol for an output transformer?) and there's an OT.

There isn't a picture of the output transformer, but the rubber grommets for the OT wires are either side of the 6V6 with wires clearly shown and labelled. As lots of layouts are set out this way that doesn't seem unusual?

I only picked the layout because others seem to have had good success (with the caveat that the layout is unclear on what filter cap and OT values to use, and has an easy to miss connection on the speed pot). As I've already mentioned, I haven't had a chance to go through the schematic to check but a quick look seems to confirm that the cap can in the layout is the 3 x 20uF 450V caps from the fender schematic.

As this is for a *future* build I'm not particularly concerned about going through it now; will get the 18W build up and running first.